The theory suggests that the reduction of game meat, fish, and some plants from the diet resulted in skin turning light many thousands of years after settlement in Eurasia.
Research by Nina Jablonski suggests that an estimated time of about 10, to 20, years is enough for human populations to achieve optimal skin pigmentation in a particular geographic area but that development of ideal skin coloration may happen faster if the evolutionary pressure is stronger, even in as little as generations. One of the most recently proposed drivers of the evolution of skin pigmentation in humans is based on research that shows a superior barrier function in darkly pigmented skin.
Most protective functions of the skin, including the permeability barrier and the antimicrobial barrier, reside in the stratum corneum SC and the researchers surmise that the SC has undergone the most genetic change since the loss of human body hair. Natural selection would have favored mutations that protect this essential barrier; one such protective adaptation is the pigmentation of interfollicular epidermis , because it improves barrier function as compared to non-pigmented skin.
In lush rainforests, however, where UV-B radiation and xeric stress were not in excess, light pigmentation would not have been nearly as detrimental. This explains the side-by-side residence of lightly pigmented and darkly pigmented peoples. Population and admixture studies suggest a three-way model for the evolution of human skin color, with dark skin evolving in early hominids in Africa and light skin evolving partly separately at least two times after modern humans had expanded out of Africa.
For the most part, the evolution of light skin has followed different genetic paths in Western and Eastern Eurasian populations. Two genes however, KITLG and ASIP, have mutations associated with lighter skin that have high frequencies in Eurasian populations and have estimated origin dates after humans spread out of Africa but before the divergence of the two lineages.
The understanding of the genetic mechanisms underlying human skin color variation is still incomplete, however genetic studies have discovered a number of genes that affect human skin color in specific populations, and have shown that this happens independently of other physical features such as eye and hair color.
Different populations have different allele frequencies of these genes, and it is the combination of these allele variations that bring about the complex, continuous variation in skin coloration we can observe today in modern humans. Population and admixture studies suggest a 3-way model for the evolution of human skin color, with dark skin evolving in early hominids in sub-Saharan Africa and light skin evolving independently in Europe and East Asia after modern humans had expanded out of Africa.
All modern humans share a common ancestor who lived around , years ago in Africa. For the most part, the evolution of light skin has followed different genetic paths in European and East Asian populations.
They are thought to have originated after humans spread out of Africa but before the divergence of the European and Asian lineages around 30, years ago. A number of genes have been positively associated with the skin pigmentation difference between European and non-European populations. A variation in TYR has also been identified as a contributor. Research indicates the selection for the light-skin alleles of these genes in Europeans is comparatively recent, having occurred later than 20, years ago and perhaps as recently as 12, to 6, years ago.
Neolithic farmers entering Europe at around the same time were intermediate, being nearly fixed for the derived SLC24A5 variant but only having the derived SLC45A2 allele in low frequencies. The SLC24A5 variant spread very rapidly throughout central and southern Europe from about 8, years ago, whereas the light skin variant of SLC45A2 spread throughout Europe after 5, years ago. A number of genes known to affect skin color have alleles that show signs of positive selection in East Asian populations.
Tanning response in humans is controlled by a variety of genes. Oculocutaneous albinism OCA is a lack of pigment in the eyes, skin and sometimes hair that occurs in a very small fraction of the population. In hominids the parts of the body not covered with hair, like the face and the back of the hands, start out pale in infants and turn darker as animals are exposed to more sun.
All human babies are born pale, regardless of what their adult color will be. In humans, melanin production does not peak until after puberty. The skin of children becomes darker as they go through puberty and experience the effects of sex hormones. In some people, the armpits become slightly darker during puberty. The interaction of genetic, hormonal, and environmental factors on skin coloration with age is still not adequately understood, but it is known that men are at their darkest baseline skin color around the age of 30, without considering the effects of tanning.
Around the same age, women experience darkening of some areas of their skin. Human skin color fades with age. Humans over the age of thirty experience a decrease in melanin-producing cells by about 10 to 20 percent per decade as melanocyte stem cells gradually die. The skin of face and hands has about twice the amount of pigment cells as unexposed areas of the body, as chronic exposure to the sun continues to stimulate melanocytes.
The blotchy appearance of skin color in the face and hands of older people is due to the uneven distribution of pigment cells and to changes in the interaction between melanocytes and keratinocytes.
It has been observed that adult human females are consistently lighter in skin pigmentation than males in the same population. Breastfeeding newborns, whose skeletons are growing, require high amounts of calcium intake from the mother's milk about 4 times more than during prenatal development ,  part of which comes from reserves in the mother's skeleton.
Adequate vitamin D resources are needed to absorb calcium from the diet, and it has been shown that deficiencies of vitamin D and calcium increase the likelihood of various birth defects such as spina bifida and rickets. Natural selection has led to females with lighter skin than males in all indigenous populations because women must get enough vitamin D and calcium to support the development of fetus and nursing infant and to maintain their own health.
The sexes also differ in how they change their skin color with age. Men and women are not born with different skin color, they begin to diverge during puberty with the influence of sex hormones. Uneven pigmentation of some sort affects most people, regardless of bioethnic background or skin color. Skin may either appear lighter, or darker than normal, or lack pigmentation at all; there may be blotchy, uneven areas, patches of brown to gray discoloration or freckling.
Apart from blood-related conditions such as jaundice , carotenosis , or argyria , skin pigmentation disorders generally occur because the body produces either too much or too little melanin. Various types of albinism are a result of genetic mutations affecting different parts of the melanin production pathway. In a person with albinism, melanocytes can be entirely absent, or fail to produce melanin, or melanosomes can fail to mature and be transferred to keranocytes. The ability to produce melanin in patches around the body is a condition known as vitiligo.
Some types of albinism affect only the skin and hair, while other types affect the skin, hair and eyes, and in rare cases only the eyes. All of them are caused by different genetic mutations.
Albinism is a recessively inherited trait in humans where both pigmented parents may be carriers of the gene and pass it down to their children. Albinism is a serious problem in areas of high sunlight intensity, leading to extreme sun sensitivity, skin cancer , and eye damage. Albinism is more common in some parts of the world than in others, but it is estimated that 1 in 70 humans carry the gene for OCA. Albinos often face social and cultural challenges even threats , as the condition is often a source of ridicule, racism, fear, and violence.
Many cultures around the world have developed beliefs regarding people with albinism. Albinos are persecuted in Tanzania by witchdoctors , who use the body parts of albinos as ingredients in rituals and potions, as they are thought to possess magical power.
Vitiligo is a condition that causes depigmentation of sections of skin. It occurs when melanocytes die or are unable to function. The cause of vitiligo is unknown, but research suggests that it may arise from autoimmune , genetic, oxidative stress , neural, or viral causes.
Increased melanin production, also known as hyperpigmentation , can be a few different phenomena:. Aside from sun exposure and hormones, hyperpigmentation can be caused by skin damage, such as remnants of blemishes, wounds or rashes. The most typical cause of darkened areas of skin, brown spots or areas of discoloration is unprotected sun exposure.
Once incorrectly referred to as liver spots , these pigment problems are not connected with the liver. On lighter to medium skin tones, solar lentigenes emerge as small- to medium-sized brown patches of freckling that can grow and accumulate over time on areas of the body that receive the most unprotected sun exposure, such as the back of the hands, forearms, chest, and face.
For those with darker skin colors, these discolorations can appear as patches or areas of ashen-gray skin. Melanin in the skin protects the body by absorbing solar radiation. In general, the more melanin there is in the skin the more solar radiation can be absorbed. Excessive solar radiation causes direct and indirect DNA damage to the skin and the body naturally combats and seeks to repair the damage and protect the skin by creating and releasing further melanin into the skin's cells.
With the production of the melanin, the skin color darkens, but can also cause sunburn. The tanning process can also be created by artificial UV radiation. There are two different mechanisms involved. Firstly, the UVA-radiation creates oxidative stress, which in turn oxidizes existing melanin and leads to rapid darkening of the melanin, also known as IPD immediate pigment darkening. Secondly, there is an increase in production of melanin known as melanogenesis. The tan that is created by an increased melanogenesis lasts much longer than the one that is caused by oxidation of existing melanin.
Tanning involves not just the increased melanin production in response to UV radiation but the thickening of the top layer of the epidermis, the stratum corneum. A person's natural skin color affects their reaction to exposure to the sun. Generally, those who start out with darker skin color and more melanin have better abilities to tan. Individuals with very light skin and albinos have no ability to tan. Modern lifestyles and mobility have created mismatch between skin color and environment for many individuals.
Vitamin D deficiencies and UVR overexposure are concerns for many. It is important for these people individually to adjust their diet and lifestyle according to their skin color, the environment they live in, and the time of year.
The following list shows the six categories of the Fitzpatrick scale in relation to the 36 categories of the older von Luschan scale: Dark skin with large concentrations of melanin protects against ultraviolet light and skin cancers; light-skinned people have about a tenfold greater risk of dying from skin cancer, compared with dark-skinned persons, under equal sunlight exposure. Furthermore, UV-A rays from sunlight are believed to interact with folic acid in ways that may damage health.
Midday was a time when people stayed in the shade and had the main meal followed by a nap,  a practice similar to the modern siesta. While UV rays can cause skin cancer, because skin cancer usually affects people after they have had children, it likely had little effect on the evolution of skin color because evolution favors changes that improve reproductive success.
There is also a third factor which affects skin color: That means that some Arctic peoples, such as native peoples of Alaska and Canada, can afford to remain dark-skinned even in low UV areas. In the summer they get high levels of UV rays reflected from the surface of snow and ice, and their dark skin protects them from this reflected light.
Species Fossils Mystery Skull Interactive. I Came From Where? Nature has selected for people with darker skin in tropical latitudes, especially in nonforested regions, where ultraviolet radiation from the sun is usually the most intense. Melanin acts as a protective biological shield against ultraviolet radiation. By doing this, it helps to prevent sunburn damage that could result in DNA changes and, subsequently, several kinds of malignant skin cancers.
Melanoma in particular is a serious threat to life. In the United States, approximately 54, people get this aggressive type of skin cancer every year and nearly 8, of them die from it. Those at highest risk are European Americans. They have a 10 times higher risk than African Americans. Ultraviolet radiation reaching the earth usually increases in summer and decreases in winter. The skin's ability to tan in summertime is an acclimatization to this seasonal change.
Tanning is primarily an increase in the number and size of melanin granules due to the stimulation of ultraviolet radiation. Irish boy who is essentially unable to tan While skin tanning is often most noticeable on light complexioned people, even those with very dark brown skin can tan as a result of prolonged exposure to the sun.
Some N orthwest Europeans have substantially lost the ability to tan as a result of relaxed natural selection. Their skin burns and peels rather than tans.
This is due to the fact that they produce a defective form of a skin protein Mc1r melanocortin-1 receptor which is necessary for the production of melanin.
They are at a distinct disadvantage in tropical and subtropical environments. Not only do they suffer the discomfort of readily burning, but they are at a much higher risk for skin cancer.
The same is true of albinos. It would be harmful if melanin acted as a complete shield. A certain amount of shortwave ultraviolet radiation UVB must penetrate the outer skin layer in order for the body to produce vitamin D. Simple vitamin D is converted by our bodies into two sequential forms. The last form, commonly referred to as vitamin D 3 , is needed for the intestines to absorb calcium and phosphorus from food for bone growth and repair.
Calcium is also necessary in adults to maintain normal heart action, blood clotting, and a stable nervous system. New evidence suggests that vitamin D may help prevent a wide range of cancers, including those of the colon and breasts. Vitamin D plays an additional important role in promoting the production of cathelicidin , which helps to defend our bodies against fungal, bacterial, and viral infections, including the common flu.
T oo much ultraviolet radiation penetrating the skin may cause the breakdown of fol ate in the body, which can cause anemia. Folate is derived from folic acid one of the B vitamins in our food.
Pregnant women who are deficient in folate are at a higher risk of having miscarriages and babies with neural tube defects. Because folate is needed for DNA replication in dividing cells, its absence can have an effect on many body processes, including the production of sperm cells. It may be that the ability to produce melanin was selected for in our early human ancestors because it helped preserve the body's supply of folate in addition to reducing the chances of developing skin cancer.
Human skin color ranges in variety from the darkest brown to the lightest hues. An individual's skin pigmentation is the result of genetics, being the product of both of the individual's biological parents' genetic makeup, and exposure to sun.
What Determines Skin Color? Skin color determination is an issue that has fascinated many people for a long time. It is by understanding of some of the factors that influence skin color that we can then find ways of modifying it without posing a risk to our health.
Skin color is determined primarily by the amount and type of melanin, the pigment in the skin. Variation in skin color is largely due to genetics. As a general pattern people with ancestors from tropical regions and higher altitudes (hence greater UV light exposure) have darker skin than people with ancestors from subtropical regions. Skin color is one of the most visible indicators that helps distinguish human appearance, and a new study provides more detail as to how one protein helps produce this wide palette. In researchers identified a gene called SLC24A5 as a key determinant of skin color.
Dec 16, · Dr. Keith C. Cheng, an author of the report, and his colleagues showed that the golden version of the fish gene altered production of melanosomes, the tiny black particles of . Your ancestors' skin color is the biggest factor in determining your skin tone. © iStockphoto /Donna Coleman Your ancestors' skin color has the biggest influence on your skin tone, which is determined by the biological factor of genetics.